Scratching the Dunes

At the bottom of Endurance crater are rippled dunes, and mission scientists hoped Opportunity would be able to drive down low enough to reach the outer margins of these dunes. Getting to those dune outreaches however has proven challenging since the terrain is sandy. Scientists had the difficult decision as to whether the rover might get trapped if they moved further, all the while wanting to sample the bottom of Endurance crater.

Endurance Crater dune near the Opportunity rover Credit: NASA/JPL

The terrain around the rover is heavily coated with sand and dust, so each traverse requires careful evaluation to make sure there is enough rock material to drive on with confidence. From the images available, the team determined it could safely command only about a 1-meter (3.3-foot) drive.

This drive proceeded as expected. At the end of the drive, panoramic camera images were acquired directly in front of the rover and out to the dune tendril. These images will be used to assess traversability to this sandy feature.

The wheel tracks in the banner image are an artifact of the difficult terrain faced recently by NASA’s Mars Exploration Rover Opportunity deep inside "Endurance Crater." Opportunity took the picture with its navigation camera on the rover’s 205th martian day, or sol (Aug. 21, 2004).

On the preceding sol, to avoid a potentially hazardous rock target, the rover team changed routes. Steep slopes and lack of traction when driving in this terrain caused the rover to experience up to 50 percent slip during parts of its traverse.

Opportunity ended up more than 50 centimeters (about 20 inches) downslope from the planned final position. Another shift in objective on sol 205 had Opportunity on the move again toward safer terrain. Analysis of the final drive showed the rover’s traction increasing during its latest moves.

On sol 203 the team decided to scratch the approach to the dune tendril and, instead, headed the rover back towards "Axel Heiberg" and another target named "Ellesmere" for some soil observations. The terrain between the rover and the dune tendril did not present clear evidence of rocky plates to give the rover sufficient traction.

Rather than spend more time in an attempt to scout further for an approach path, the decision was made to abandon the quest for the dune tendril.

The path of Opportunity nearing the bottom of Endurance. The challenges of clear navigation paths has frustrated attempts to get to dune tendrilsCredit: NASA/JPL

A drive of approximately 14 meters (46 feet) positioned the rover where it will be able to zero in on Ellesmere next. There was an apparent combination of slip or induced heading change, or both, due to the sandy terrain, which resulted in the rover ending up about 3 meters (about 10 feet) farther left than expected. This also caused Opportunity to unintentionally run over a patch of fine soil with some small dune-like ripples in it.

The team will be assessing this traverse error, but it is par for the course when driving this far on such sandy, sloped terrain.